JP2009044615A - Electronic camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electronic camera capable of executing suitable clamp processing even when a high resolution object is entered into an end part of a picture in a through mode. <P>SOLUTION: The electronic camera includes a black level calculation circuit 45 for calculating a black level on the basis of an image pickup signal generated from an optical black area formed adjacently to an effective area out of image pickup signals outputted from a CCD 3 and a clamp circuit 42 for clamping the image pickup signal based on the black level. A luminance level or a smear generation level of a specific evaluation area in the effective area, which is formed adjacently to the optical black area, is adopted as an evaluation value, the leakage of electric charge from the effective area to the optical black area is predicted, and in a period that the evaluation value exceeds a prescribed threshold, clamp processing is performed on the basis of the black level of an image pickup signal obtained just before the time that the evaluation value exceeds the prescribed threshold. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electronic camera, such as a digital camera, that generates an image by clamping an imaging signal output from an imaging element such as a CCD at a black level.

  In the digital camera, an optical black area (OB portion) is provided adjacent to the effective area of the CCD (3) as shown in FIG. 2, and when the shutter button is pressed, the CCD (3) is pre-exposed. As a result, among the image pickup signals obtained from the CCD (3), the level of the image pickup signal (black level) from the optical black area is acquired, and a clamp process is performed to clamp the image pickup signal based on the black level. Is done. Then, a video signal for one screen is generated based on the image pickup signal subjected to the clamp process. As a result, the luminance of the subject image is properly evaluated, and the exposure amount is set to an optimum value.

However, when high-intensity light is irradiated onto the CCD, charge leaks from the effective area to the optical black area, and the black level fluctuates. Therefore, in the conventional digital camera (see Patent Document 1), when the shutter button is pressed, the luminance evaluation value is obtained from the image pickup signal subjected to the clamp processing by the first pre-exposure, and the second pre-exposure is performed. A luminance evaluation value is obtained from an imaging signal that has been subjected to clamp processing by exposure. Based on the difference between the two luminance evaluation values, the clamp period is set to one of the optical black period and the idle feed period. As a result, the fluctuation of the clamp level of the imaging signal obtained by the final pre-exposure is prevented.
JP 2000-278613 A [H04N5 / 335]

By the way, in a digital camera, an image (through image) is displayed in real time on the monitor screen based on the image pickup signal obtained from the CCD before the shutter button is pressed, that is, when the main exposure or pre-exposure is not performed. (Through mode)
If a high-brightness object such as the sun enters the right or left edge of the screen in such a through-image display state, the conventional digital camera only responds after the shutter button is pressed. As a result, charge leakage from the optical black area occurs, the black level fluctuates, and the through image becomes abnormal. Even in the shooting mode, there is a problem that the subject is determined to be dark and an overexposed image is formed.

  Therefore, an object of the present invention is to provide an electronic camera that can perform an appropriate clamping process even when a high-luminance subject enters the end of the screen in the through mode.

The electronic camera according to the present invention calculates a black level based on an image pickup signal from an optical black area provided adjacent to an effective area among image pickup signals output from the image pickup device, and calculates the black level. A clamp process for clamping an image pickup signal as a reference is performed, and a video signal for one screen is generated based on the image pickup signal subjected to the clamp process,
Evaluation value acquisition means for acquiring an evaluation value that will change when leakage of charges from the effective area to the optical black area occurs;
In a period in which the acquired evaluation value exceeds a predetermined threshold value, a black level fixing unit is provided that provides the black level of the imaging signal immediately before the evaluation value exceeds the predetermined threshold value as a fixed value for the clamping process. .

As the evaluation value by the evaluation value acquisition means, a luminance level of a specific evaluation area provided in the vicinity of the optical black area in the effective area or a smear occurrence level in the specific evaluation area is adopted. I can do it.
Note that the luminance level and smear generation level in the specific evaluation area are values that are used for adjusting the aperture amount and smear correction in the conventional digital camera, and are therefore specifically detected for the implementation of the present invention. do not have to.

In the electronic camera of the present invention, when a high-luminance subject such as the sun enters the right or left edge of the screen in the through image display state, charge leakage from the effective area to the optical black area occurs. However, immediately before the leakage of electric charges occurs, the luminance level and smear generation level of the specific evaluation area, which is the evaluation value, increase.
Therefore, when the evaluation value exceeds a predetermined threshold, it is predicted that charge leakage from the effective area to the optical black area will occur immediately thereafter, and thereafter, imaging immediately before the evaluation value exceeds the predetermined threshold. The black level of the signal is used for the clamping process.

Therefore, even if charge leakage from the effective area to the optical black area occurs immediately after that, the black level used for the clamping process is the value immediately before the charge leakage occurs and is not affected by the charge leakage. Therefore, the clamping process using the black level stabilizes the DC component of the imaging signal, and a normal through image is obtained. Also in the shooting mode, the brightness of the subject is accurately determined and appropriate exposure can be obtained.
After that, when the high-luminance subject disappears from the screen, the evaluation value falls below a predetermined threshold value. Therefore, fixing the black level used for the clamping process is interrupted, and the black of the imaging signal obtained in real time from the optical black area A normal clamping process is executed based on the level.

In the black level fixing by the black level fixing means, the first threshold value and the second threshold value can be used. In this case, when the acquired evaluation value exceeds the first threshold value, the black level of the imaging signal immediately before the evaluation value exceeds the first threshold value is used as a fixed value for clamp processing, and the acquired evaluation value is After falling below the threshold of 2, the black level of the imaging signal obtained in real time from the optical black area is subjected to the clamping process.
Here, if the second threshold value is set to be smaller than the first threshold value, the black level can be released when the risk of charge leakage is completely eliminated.

  According to the electronic camera of the present invention, it is possible to perform an appropriate clamping process even when a high-luminance subject enters the edge of the screen in the through mode, thereby stabilizing the black level of the image pickup signal and high-quality video. Can be generated.

Hereinafter, embodiments of the present invention applied to a digital camera will be described in detail with reference to the drawings.
In the digital camera according to the present invention, as shown in FIG. 1, image light is irradiated from the optical lens (1) to the CCD (3) through the aperture unit (2), thereby obtaining an imaging signal obtained from the CCD (3). Is supplied to the one-chip ASIC (5) through the one-chip IC (4), and a video signal is generated.

The video signal generated in this way is recorded on the memory card (10) via the card I / F (9) or supplied to the monitor (12) by the video encoder (11) and displayed on the screen. .
A CPU (7) is connected to the one-chip ASIC (5), and the CPU (7) executes a predetermined calculation process using the memory (8) to the one-chip IC (4). In addition to supplying various data, a control signal for controlling the aperture unit (2) is supplied to the driver (15).

  Further, a system controller (13) is connected to the CPU (7), and the system controller (13) receives an operation signal from the shutter button (14) and sends a photographing command to the CPU (7).

  The one-chip ASIC (5) is provided with a signal generator (56), and the vertical synchronization signal Vsync and the horizontal synchronization signal Hsync are supplied from the signal generator (56) to the timing generator (55). In response to this, the timing generator (55) generates a charge read pulse, a vertical transfer pulse, a horizontal transfer pulse, and a clamp pulse.

The charge for one screen generated by the CCD (3) is read by the charge readout pulse, vertical transfer pulse and horizontal transfer pulse from the timing generator (55), and is output to the one-chip IC (4) as an imaging signal. The
As shown in FIG. 2, an optical black area (OB portion) is provided on the light receiving surface of the CCD (3) adjacent to the effective area. Includes an imaging signal component from the effective area and an imaging signal component from the optical black area (OB portion).

  As shown in FIG. 1, the imaging signal output from the CCD (3) is supplied to the clamp circuit (42) through the correlated double sampling process by the CDS circuit (41). The clamp circuit (42) clamps the imaging signal in response to a clamp pulse from the timing generator (55). In the through mode in which a moving image (through image) is displayed in real time, the timing generator (55) generates a clamp pulse during the optical black period of the imaging signal, whereby the imaging signal is clamped at the optical black level.

The clamped imaging signal is subjected to gain adjustment by an AGC circuit (43) and then converted to a digital signal (imaging data) through an A / D converter (44).
The imaging data obtained from the A / D converter (44) is supplied to the black level calculation circuit (45), and the timing generator (55) generates a clamp pulse during the optical black period, thereby generating a black level calculation circuit ( 45) calculates the black level of the optical black area using the memory (46), and supplies the result to the clamp circuit (42).

  The first signal processing circuit (51) of the one-chip ASIC (5) generates RGB data and Y data based on the imaging data supplied from the one-chip IC (4), and uses these data as the second signal processing circuit. To (52). The second signal processing circuit (52) converts RGB data and Y data into YUV data, and outputs the YUV data to the video encoder (11) via the memory (6). As a result, the video data that has undergone the predetermined encoding process is supplied to the monitor (12), and a through image is displayed on the monitor screen.

  During such a through image display period, the Y data output from the first signal processing circuit (51) is supplied to the integrating circuit (53). The integration circuit (53) integrates the Y data over a predetermined area, and outputs the integration value obtained thereby to the CPU (7). Here, the region to be integrated is a normal evaluation area set within the effective area shown in FIG. 2, and is a region where luminance evaluation is performed in the photographing mode and the through mode. In this normal evaluation area, a part of the area adjacent to the OB portion is set as a specific evaluation area, and this specific evaluation area is an object of evaluation in the prediction of charge leakage.

  When the shutter button (14) shown in FIG. 1 is pressed in the through mode, the mode is changed to the shooting mode and the actual shooting is performed. The exposure time in the through mode is held in the register (54) of the one-chip ASIC (5), and the timing generator (55) is preloaded in the CCD (3) according to the exposure time held in the register (54). Let the exposure occur.

  The timing generator (55) also generates a clamp pulse at the timing when the black level output from the black level calculation circuit (45) is input to the clamp circuit (42), and supplies the clamp pulse to the clamp circuit (42). As a result, the clamp circuit (42) clamps the imaging signal at the black level. As a result, the first signal processing circuit (51) generates Y data based on the clamped imaging signal, and the generated Y data is integrated over the normal evaluation area by the integration circuit (53). The average luminance of the normal evaluation area is obtained by

  The CPU (7) takes in the average luminance value from the integrating circuit (53), writes the value into the memory (8), and calculates the optimum aperture amount and the optimum exposure time based on the average luminance value. Then, aperture amount data indicating the calculation result is given to the driver (15). Thereby, the aperture amount of the aperture unit (2) is adjusted.

  When the update of the exposure time and the adjustment of the aperture amount are completed, the timing generator (55) performs the main exposure of the CCD (3) according to the optimum exposure time data set in the register (54), and sends a clamp pulse to the clamp circuit ( 42). The imaging signal generated by the main exposure is clamped at the black level by the clamp circuit (42). The clamped imaging signal is converted into imaging data through AGC processing by the AGC circuit (43), and thereafter, the same processing as described above is performed in the first signal processing circuit (51) and the second signal processing circuit (52). Applied. As a result, YUV data based on the main exposure is generated, and the UYV data is recorded on the memory card (10) through the card I / F (9).

Specifically, the CPU (7) executes the procedures shown in FIGS. 3 and 5 in the above-described through mode and photographing mode.
When the power of the digital camera is turned on, first, in step S1 of FIG. 3, initial settings such as setting of the through mode, setting of the shutter speed and aperture value, setting of the OB clamp position, setting of the OB clamp level (black level), etc. Is done.

  Next, in step S2, the luminance information of the normal evaluation area is acquired, and in step S3, the luminance level of the normal evaluation area is calculated. In step S4, the black level is calculated, and the result is written in the memory (46) shown in FIG.

Subsequently, in step S5 of FIG. 3, the OB clamp level is set based on the calculated black level. In step S6, the shutter speed and the aperture value are set, and then the process proceeds to step S7.
In step S7, the luminance information of the normal evaluation area is acquired, and in step S8, the luminance level of the normal evaluation area is calculated. In step S9, the luminance level of the specific evaluation area is calculated. Note that the luminance level of the specific evaluation area can be calculated using the luminance information acquired in step S7.

  Thereafter, in step S10, it is determined whether or not the OB clamp level (black level) is fixed. If no, the process proceeds to step S11, and the luminance level of the specific evaluation area has a predetermined first threshold value TH1. Judge whether or not it exceeds. If NO is determined, the process proceeds to step S15 to set the OB clamp position. In step S16, the black level is calculated and the result is written in the memory, and then the process returns to step S5.

If a high-luminance object such as the sun enters the specific evaluation area in the process of repeating the above processing, the luminance level of the specific evaluation area immediately before the leakage of charge from the effective area to the optical black area occurs. Will rise.
As a result, the luminance level exceeds the first threshold value TH1 in step S11 of FIG. 3, and the process proceeds to step S12. In step S12, the black level is read from the memory (46) shown in FIG. 1 and supplied to the clamp circuit (42). Thus, the clamping process is executed based on the black level immediately before the luminance level exceeds the first threshold value TH1.
That is, the process proceeds from step S12 to step S5 in FIG. 3 to set the OB clamp level (fix the black level).

  Thereafter, the determination at Step S10 is YES, and the process proceeds to Step S13, where it is determined whether or not the luminance level of the specific evaluation area exceeds a second threshold value TH2 that is smaller than the first threshold value TH1. At this time, if a high-luminance subject still exists in the specific evaluation area, it is determined as YES in step S13, and in step S14, the black level is read from the memory (46) shown in FIG. Based on the above, the clamping process is executed.

  If the high-luminance subject disappears from the specific evaluation area and the luminance level of the specific evaluation area decreases, it is determined NO in step S13, and the process proceeds to step S15. In step S15, the OB clamp position is newly set. In step S16, the black level calculation circuit (45) shown in FIG. 1 calculates the black level from the image data obtained at that time, and the result is stored in the memory ( 46) and supply to the clamp circuit (42). As a result, the setting of the OB clamp level (release of black level fixation) is performed in step S5 in FIG. 3, and the normal clamping process is resumed.

  According to the above-described processing, when a high-luminance object such as the sun enters the right end of the screen in the through image display state, charge leakage from the effective area to the optical black area may occur. Since the luminance level of the specific evaluation area is increased immediately before this leakage of electric charge occurs, the luminance level of the specific evaluation area is determined to be the first level from the normal clamping process according to the determination in step S11 of FIG. The process proceeds to the clamping process based on the black level immediately before exceeding the threshold.

  Therefore, even if charge leakage from the effective area to the optical black area occurs immediately after that, the black level used for the clamping process is the value immediately before the charge leakage occurs and is not affected by the charge leakage. Therefore, the clamping process using the black level stabilizes the black level as a reference for the video reproduction process, and a normal through image can be obtained. Also in the shooting mode, the brightness of the subject is accurately determined and appropriate exposure can be obtained.

After that, when the high-luminance subject disappears from the specific evaluation area, the luminance level of the specific evaluation area is lowered, so that the normal clamp is performed from the clamp processing based on the fixed black level according to the determination in step S13 of FIG. Return to processing. At this time, since the second threshold value is set smaller than the first threshold value, the black level can be unfixed when the risk of charge leakage is completely eliminated.
The first threshold value and the second threshold value can be set to the same value.

When the shutter button (14) shown in FIG. 1 is pressed during the process in the above-described through mode, the process shifts to the shooting mode and the process shown in FIG. 5 is executed.
First, at step S21, the OB clamp level is maintained at a set value, and after performing pre-exposure at step S22, an evaluation value for photographing is calculated at step S23. Based on the result, the shutter speed is calculated at step S24. And set the aperture value.
Thereafter, the main exposure is performed in step S25, the video data obtained by the main exposure is compressed in step S26, and the compressed video data obtained in this way is recorded in the memory card in step S27.

In the through mode, the process shown in FIG. 4 can be adopted instead of the process shown in FIG.
In the process shown in FIG. 4, in place of step S9 in FIG. 3, in step S9 ′, information representing the smear level is acquired, and in step S9 ″, the smear level is calculated based on the information. In step S11 ′, the smear level is compared with the first threshold value TH1 ′, while in step S13 ′, the smear level is compared with the second threshold value TH2 ′. It is set smaller than the threshold value TH1 ′.

  Similarly, in the processing shown in FIG. 4, when a high-luminance subject such as the sun enters the right end of the screen in the through image display state, charge leakage from the effective area to the optical black area may occur. However, since the smear level in the specific evaluation area increases immediately before this leakage of electric charge occurs, the brightness level of the specific evaluation area is determined from the normal clamping process by the determination in step S11 ′ of FIG. Shifts to the clamping process based on the black level immediately before the first threshold value is exceeded.

Therefore, even if there is a charge leak from the effective area to the optical black area immediately after that, the black level used for the clamping process is not affected by the charge leakage, so the clamping process using the black level The black level, which is the standard for video playback processing, is stabilized, and a normal through image can be obtained.
After that, when the high-luminance subject disappears from the specific evaluation area, the luminance level of the specific evaluation area is lowered, so that the determination from step S13 ′ in FIG. The normal clamping process is resumed.

  As described above, according to the digital camera of the present invention, even when a high-luminance subject enters the edge of the screen in the through mode, an appropriate clamping process can be performed by fixing the black level. The black level of the signal is stable and high-quality video can be generated.

  In addition, each part structure of this invention is not restricted to the said embodiment, A various deformation | transformation is possible within the technical scope as described in a claim. For example, when the optical black area is provided on the left side of the screen, the specific evaluation area is set at the left end of the screen adjacent to the optical black area. Further, as the image pickup element, a CMOS type image sensor can be adopted instead of the CCD (3).

It is a block diagram showing the structure of the digital camera which concerns on this invention. It is a figure which shows the effective area and optical black area of CCD. It is a flowchart showing the process in the through mode of the digital camera which concerns on this invention. It is a flowchart showing the other process example in through mode. It is a flowchart showing the process in imaging | photography mode.

Explanation of symbols

(1) Optical lens
(2) Aperture unit
(3) CCD
(42) Clamp circuit
(45) Black level calculation circuit
(46) Memory
(55) Timing generator

Claims (5)

Clamp that calculates the black level based on the image signal from the optical black area provided adjacent to the effective area, and clamps the image signal based on the black level, among the image signals output from the image sensor In an electronic camera that performs processing and generates a video signal for one screen based on an imaging signal subjected to clamping processing,
Evaluation value acquisition means for acquiring an evaluation value that will change when leakage of charges from the effective area to the optical black area occurs;
In a period in which the acquired evaluation value exceeds a predetermined threshold value, a clamp value fixing unit is provided that provides the black level of the imaging signal immediately before the evaluation value exceeds the predetermined threshold value as a fixed value for the clamping process. An electronic camera characterized by that.   The electronic camera according to claim 1, wherein the evaluation value to be acquired by the evaluation value acquisition unit is calculated for a specific evaluation area provided in the vicinity of the optical black area in the effective area.   The electronic camera according to claim 1, wherein the evaluation value acquisition unit employs, as the evaluation value, a luminance level of a specific evaluation area provided in the vicinity of the optical black area in the effective area. .   The said evaluation value acquisition means employ | adopts the generation | occurrence | production level of the smear in the specific evaluation area provided close to the said optical black area as the said evaluation value among the said effective areas. Electronic camera.   The clamp value fixing means has a first threshold value and a second threshold value, and when the acquired evaluation value exceeds the first threshold value, the clamp signal fixing means immediately before the evaluation value exceeds the first threshold value. The black level is used as a fixed value for the clamping process, and after the acquired evaluation value is below the second threshold, the black level of the imaging signal obtained in real time from the optical black area is used for the clamping process. The electronic camera according to any one of claims 1 to 4, wherein:

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